1. Field of the Invention
This invention relates generally to valves and specifically to a pressure-compensated directional control valve assembly. The valve assembly according to the invention is particularly well adaptable for use as a hydraulic power steering valve in some off-highway work machines.
2. Description of the Prior Art
The control valves for hydraulic power steering systems have been known and used extensively which essentially are combinations of a directional control valve and a flow control valve or of a directional control valve and a flow divider. These control valves tend to invite great energy loss at high engine speed and to give rise to hunting through an increase in steering load pressure. A pressure-compensated directional control valve has also been suggested for use in a hydraulic power steering system, but it also is subject to considerable energy loss at high engine speed.
The hydraulic steering control valve in some off-highway working vehicles is desired to deliver pressurized fluid not only to the steering cylinder but also to an additional actuator such as an implement hoist cylinder. This is desirable because the steering cylinder need not demand the fluid pressure at all times during the operation of the work vehicle. The designing of such a control valve requires special consideration because the available pump pressure and delivery is subject to change with engine speed and because the additional actuator also makes a variable demand on the pump pressure.